Hello,
Regarding this:
"TTD: The narrative of Genesis tells us that Isaac had a brother (a sibling)
named Ishmael, but would Collver@msn.com be incorrect about the
MONOGHNHS-sibling issue, since the word MONOGHNHS is not used in the LXX
text of Genesis to describe the relationship of Abraham to Isaac but is used
later in the book of Hebrews?"

I should've been more precise. I should have said that when MONOGHNHS is used
it is the only child from that mother or father. This would not rule out other
siblings from a different mother or father. What is interesting with Abraham
is that Isaac is the MONOGHNHS ... he had another Son by another woman. I
would wiggle out of this one by stating that Isaac was the only (MONO) son of
the promise.
Regarding Jesus, he is MONOGHNHS of the Father not Mary or Joseph. This is an
important distinction since he is Mary's first-born...
Sincerely,
Albert B. Collver, III